Storage ring



Sept. 26, 1967 I J. P. BLEWETT 3,344,357

, STORAGE RING Filed July 13, 1964' 2 Sheets-Sheet 1 TYPE I MAGNET G3 7 52 29 BENDING MAGNET/ TYPE I I 13 X/ X MAGNET 33 d l 1 41 X A 2 H l TYPE 11 MAGNE V V QUADRVUPOLE 25 TYPE III, MAGNET TYPE 1 MAGNET A 33 v 23 BENDING MAGNET l5 TYPE 11 MAGNET TYPE I MAGNET QUADRUPOLE I TYPEII MAGNET BENDING MAGNET I .1- I I .u I l I I l\] I L L' 46'\ o To CENTER A c 0F RING 1 A N I I C: I 33 I I I- WI. 23 Fig.2

INVENTOR.

JOHN P BLEWETT United States Patent 3,344,357 STGRAGE RING John P. Blewett, Heliport, N.Y., assignor to the United States of America as represented by the United States Atomic Energy Commission Filed July 13, 1964, Ser. No. 382,424 5 Claims. (Cl. 328233) ABSTRACT OF THE DISCLQSURE Method and apparatus for stacking and merging high energy beams of charged particles confined along an endless equilibrium axis in separate function bending and strong focusing magnets by selectively sequentially producing opposite magnetic particle bending fields with adjacent, separate function magnetic means disposed transverse to said axes and azimuthally equally spaced from said magnets for displacing and maintaining said particles in distinct beams along said axis with a low energy spread and selectively merging the two beams along said axis into a high density beam.

This invention was made under, or in connection with a contract with the United States Atomic Energy Commission.

In the field of high energy physics it has often been desirable to displace high energy charged particle beams. Various proposals have been made and used to accom plish such displacement including those arrangements where a high energy, strong focused beam of particles is radially displaced by a radio-frequency signal. While these arrangements are useful and can accomplish the desired displacement they have produced an appreciable energy spread. It has been universally recognized, therefore, that it would be advantageous to displace high energy, strong focused, charged particle beams without appreciable energy spread. Additionally, it has been advantageously simply and easily to provide for the displacement of two of these beams and the merging thereof into a single high intensity beam.

By this invention there is provided method and apparatus for the injection, stacking and merging of high energy beams of strongly focused particles in distinct equilibrium orbits in the multiple bev. range up to 30 bev. or more. The method and construction involved in this invention utilize standard and well-known techniques and apparatus and are highly flexible for a wide range of applications, beam energies, particle equilibrium orbits, strong focusing apparatus and magnetic means. More particularly, this invention contemplates a system of strong focusing magnetic lenses and separate function bending magnets having therebetween separate function magnetic means for changing the field in the inner and outer regions of the separate function bending magnets. In one embodiment a split magnet is provided azimuthally of the axis of the main separate function bending magnet for changing the field on opposite sides of this axis. With the proper manipulation of the magnets, as described in more detail hereinafter, the field is properly weakened and strengthened for achieving low energy spread, multi-turn injection, betatron phase space stacking, separate orbits displaced from one another, merging of the two orbits, high beam intensities and high intensity beam storage for long periods of time.

It is an object of this invention, therefore, to provide an improved method and apparatus for displacing strongly focused beams of high energy particles;

It is another object to fill the synchrotron phase space in a high energy, strong focusing system for a beam of charged particles;

3,344,357 Patented Sept. 26, I967 It is another object to provide a high intensity beam of charged particles having a small energy spread;

It is another object of this invention to provide improved method and apparatus for the injection and storage of high energy charged particles;

It is another object to provide a magnetic strong focusing and separate function bending system in which the stacking of particles in a beam takes place;

It is another object of this invention to provide two charged particle beam equilibrium orbits;

It is another object to merge the equilibrium orbits of two strongly focused, high energy beams of charged particles;

Still another object is to provide multi-turn injection in a high energy strong focusing system.

The above and further novel features of this invention will appear more fully from the following detailed description when the same is read in connection with the accompanying drawings. It is to be expressly understood, however, that the drawings are not intended as a definition of the invention but are for the purpose of illustration only.

In the drawings where like parts are marked alike:

FIG. 1 is a partial diagrammatic illustration of the principles involved in this invention showing the magnetic strong focusing lens and bending system of this invention;

FIG. 2 is a partial schematic View of the bending magnet of FIG. 1 through AA having superimposed thereon the split magnet of FIG. 1 through BB;

FIG. 3 is a cross-sectional view of the bending magnet of FIG. 2;

FIG. 4 is a cross-sectional view of the split magnet of FIG. 2.

It is known that beams of high energy charged particles may be piped over long distances by using strong focusing systems of quadrupole magnetic lenses. A quadrupole magnetic lens is shown and discussed in The Strong- Fccusing SynchrotronA New High Energy Accelerator by E. D. Courant, M. S. Livingston and H. S. Snyder, in the Physical Review, vol. 88, No. 5, pages 1190-1196, Dec. 1, 1952. Figure 9 of that paper illustrates a lens of this type. Focusing of the particles by this type of lens system is based on the fact that all the particles making up a particular beam have identical momentum along an equilibrium axis.

Disposed along the length of this axis are a plurality of quadrupole lens pairs M M and M each quadrupole of each pair, as is understood in the art, tending to focus the particles passing therethrough in some particular transverse plane, such as either an X plane or a Y plane at right angles thereto. Each lens pair consists of two quadrupole magnetic lenses to obtain complete focusing in all planes. All the particles intersect the equilibrium axis at places designated converging or focal points since although the individual particles have different directions of momentum they have identical total momentum as described, for example, in US. Patent 3,056,023.

The particles and mathematics of such focusing systems are well known in the art such that this axis may be circular. To this end the particle paths are bent or deflected by separate function bending magnets described, for example, in US. Patent 2,736,799, FIG. 3 of that patent illustrates a uniform gap H-shaped bending magnet of this type. These magnets may be uniform gap C-shaped magnets, however, as is well known. Bending of the particles by both these uniform gap magnet configurations respectively, is based on the fact that all the particles making up a particular beam are deflected at right angles to the direction of the field in the space between the north and south poles of the bending magnets by the force of the field in this space, as is well known.

The transverse acceleration of the particles by the magnetic field force varies inversely as the momentum. With proper apparatus and appropriately sized apertures, it becomes possible, if desired to bend the particles in a circular orbit of the desired diameter. Other references showing and describing these elements or the circular strong focused equilibrium orbits and the combination of quadrupole strong focusing and separate function bending magnets are US. patent application S.N. 207,445 filed July 3, 1962 by T. L. Collins, now US. Patent 3,171,025 and US. Patent 2,736,799.

The invention hereinafter described utilizes a strong focusing and separate function bending system of this type in which spaces between the quadrupole focusing lenses and bending magnets through which the particles pass are subjected to magnetic bending fields in a manner described hereinafter in connection with particular configuration of these magnetic focusing and bending systems.

In order to explain how the method and apparatus of this invention accomplishes the function of displacing the particles in separate and high intensity orbits, reference is made to FIG. 1, wherein is illustrated a main, central, circular equilibrium axis 11, which is partially shown for ease of explanation. Disposed along the length of this axis 11 is an annular array of quadrupole lens pairs. For ease of explanation only one quadrupole lens pairs 1315 is shown. Each quadrupole of each pair, as is understood in the art, tends to focus the particles passing therethrough in some particular transverse plane, such as either the horizontal X plane of axis 11 or the vertical Y plane at right angles thereto. It will be seen that the first lens has a first focal point at a source (i.e. axis 11) so that the particles are received and are focused in one plane in the first lens 13 to intersect at a second focal point 21 on the equilibrium axis 11 in main separate function bending magnet 23. This bending magnet deflects the particles into the next or second lens 15, whose first focal point 25 is located on the equilibrium axis 11 to receive these particles and focus them at a second focal point on axis 11 in the next or second plane. This results in strong focusing of the particles for their transport into the next main bending magnet 27, for providing another source on axis 11 for the next strong focusing quadrupole lenses and the next separate function main bending magnets, until the particles return to main bending magnet 29 and quadrupole lens 13 for the beginning of a new cycle as described above.

Should split magnetic fields be selectively applied to the particles in the beam along axis 11 by split magnets 33 in between a quadrupole magnet (such as lens 13) and a main bending magnet (such as bending magnet 23) in the configuration indicated in FIG. 2 of the fields of the labeled poles, the outside and inside of this main bending magnet from axis 11 will be strengthened and weakened accordingly and new equilibrium orbits will exist at points B and C respectively. The displacement of point B from point A corresponding to axis 11 is greater than the displacement of point C from point A since point C is closer to the center of the circle of axis 11. If no magnetic field is applied by split magnet 33 then one equilibrium axis A is present coinciding with axis 11. Over a plurality of such stages, suitable correcting magnets may be provided and adjustments in the magnetic fields produced by the magnets are made to achieve the desired axes. To this end conventional electrostatic probes 41 and 41 are provided for determining and adjusting the magnet fields for changing the beam axes remotely, manually or automatically.

In a practical arrangement for accomplishing separate orbits of high energy charged particles, main bending magnets, comprising magnets 23, 27, 29 etc. are separated function magnets and their main or primary equilibrium orbit is at A. Azimuthally displaced from these magnets are split, separate function bending magnets 33 whose cross-section is indicated by dotted lines 43 in FIG. 2. The section of magnets 33 labeled I weakens the field in the outer region and the section of magnets 33 labeled II strengthens the field in the inner part of their adjacent main magnets comprising magnets 23, 27, 29 etc. respectively. When magnet sections I and II are turned on to suitable strengths, new equilibrium orbits exist at B and C.

Advantageously both magnet sections I and II of magnets 33 and main bending magnets 23, 27, 29 etc. have flat adjacent iron poles N and S forming open ended, uniform, parallelepiped gaps 45, 45' and 46 respectively. Also the main magnets (e.g. 23, 27, 29) and magnet sections I and II of magnets 33 advantageously have connecting back iron legs 47, 48 and 4.8, respectively. The theory of operation of these back legs is like that of the abovementioned typical C-shaped magnets. The coils 50, 51 and 51' are disposed on either side of the pole legs, as shown in FIGS. 3 and 4. The upper coils are energized in the opposite direction, respectively, to produce adjacent north and south poles across gaps 45, 45 and 46 respectively as shown in FIG. 2.

To obtain the storage of particles in separate and energized orbits the following sequence is followed. Magnet section I is turned on and an injected beam begins circulating in orbit B; magnet section I is turned off and the beam circulation moves to orbit A; magnet section II is turned on and the beam circulation moves to orbit C; magnet section I is turned on and another injected beam begins circulating in orbit B; magnet sections I and II are slowly turned off and the two beams circulating in orbits B and C merge or coalesce into one circulating beam in orbit A; magnet section II is turned on and this single beam circulation moves to orbit C; magnet section I is turned on and more particles are injected to begin circulating in orbit B, and so forth.

This sequence Will not violate Liouvilles theorem since as the particle stacking proceeds the maximum betatronoscillation amplitude will build up. In a 33 bev. proton strong focusing storage ring 52 a small betatron-oscillation is provided in an evacuated enclosure tube 53 so that the particles, such as protons, traveling close to the speed of light will not hit the sides of this beam enclosing evacuated tube 53. Advantageously, the beam oscillates with a pre-deterrnined small betatron oscillation along the tube equilibrium axis with a wave length only up to about 300 feet long and a betatron frequency only up to about 3 megacycles per second for full beam energy, where the beam diameter is about .25 inch on the average.

In multi-turn injection by this method the maximum value of turns is given by the ratio:

(Vertical acceptance area) (Horizontal acceptance area) (Vertical beam emittance) (Horizontal beam emittance) Thus for a final beam area 6 cm. x 1. cm., in a 7 x 15 cm. evacuated tube 53, whose construction is substantially similar to the evacuated tube in the Brookhaven National Laboratory 33 bev. Alternating Gradient Synchrotron or AGS, as is well known in the art, the acceptance areas are 19.3 and 0.54 cm.-mrad. Likewise, the emittance area for this invention like the AGS, which is about 6 mm. in diameter, is 0.19 in both planes. Hence in a 1 x 1 cm. area one can fill the phase space with this invention by injecting a maximum of:

Thus high particle intensities are provided by this invention. Moreover this filled space, in accordance with this invention will have a small energy spread, at least as low as the injector. Additionally, this invention provides high energy, high intensity, low energy spread beams for internal and external targeting and, by duplication two beams for colliding beam experiments.

In the operation of one example of this invention, source 61 provides charged particles in a stream for stor- =290 turns age ring 52. A suitable source is the Brookhaven hydrogen proton AGS described in The Brookhaven Alternating Gradient Synchrotron by John P. Blewett reprinted in the 1960 International Convention Record, Part 9, having suitable magnetic piping means 81. This AGS has 13,000 gauss bending magnets for accommodating protons having a magnetic rigidity of 34 bev./c. The extracted beam is a small diameter beam of up to 30 bev. or more with intensities of up to about protons/cm. or more. The radius of this AGS ring is 421.45 feet. However, other cyclic high energy accelerators, such as the Fixed Field Alternating Gradient (FFAG) accelerator, for protons or any other charged atomic particles, may be used.

The accelerated particles are extracted from source 61 by conventional extraction means 63, one such means being the magnetic extractor described in US. Patent 3,128,405. This injects the particles into the annular evacuated tube 53 of storage ring 52, whose confining and focusing magnets are maintained at the proper constant field strength to keep the particles circulating in a beam in tube 53 for long periods of time without hitting the inside walls of the tube 53. The length of the main bending magnets (e.g. magnet 23) is the same as the length of split magnet 33, shown in FIG. 1. Additionally, the gap dimensions of the gap 46 in the main bending magnets (e.g. magnet 23) are the same as the dimensions across the combined gaps 45 and 45' in split magnets 33. In general, the above described ring 52 has iron and maximum gap between poles the same as the AGS iron and maximum gap. The field strengths used in this invention can be high in the main magnets (e.g. magnet 23) and split magnets 33 since the above described uniform gap between the magnet poles provide small adverse eflects of saturation. Also, the gaps in this invention can be wide to accommodate high beam intensities since the fields across the gaps of the magnets of this invention are very uniform. These fields are suitably constant in correspondence with the constant particle momentum of the particles in ring 52 wherein the particles coast at a constant velocity without any RF acceleration being required.

Advantageously the pressure in tube 53 is at a vacuum of 0.9 10 torr or less so as to maintain low scattering for maintaining a circulating beam at orbits B and Chaving an initial intensity of 10 protons/cm. for at least eight minutes. In this regard higher vacuums will reduce scattering for maintaining a circulation of the beam for hours or more.

Each beam at orbit A, B and C, respectively, is in this example about /2 inch in diameter so the distance between these orbits is greater than the beam diameters and their betatron wave amplitudes. In this example the distance between orbits A and C is about 6 inches and between orbits A and B about 6 inches for 30 bev. protons.

The coils 50 of the main separate function bending magnets, e.g. magnets 23 are shown in FIG. 3. These coils and the coils 51 of split magnet section I, shown in FIG. 4, are energized to bend the paths of the injected particles in the first outward equilibrium orbit in tube 53 relative to the center of storage ring 52. Then these coils 51 are de-energized while coils 50 remain energized to bend the paths of the particles in tube 53 in the second central equilibrium orbit 11, which is slightly smaller in diameter than the first orbit. The coils 50 remain energized and the coils 51 of magnet section II, shown section H, shown in FIG. 4, are energized to bend the paths of the particles in tube 53 in a third inward equilibrium orbit, which is slightly smaller than the second or central equilibrium orbit 11. The beam is thus captured in the inner orbit to free the outer portion of the tube 53 for the injection of another beam in the tube 53. The gaps 46, 45 and 45' of the main bending magnets (e.g. magnet 23) and magnet sections I and II are Wide enough between their poles and across their faces to accommodate tube 53 and therein the two beams in their three distinct and separate orbits. Since the main bending magnets, such as magnets 23 and magnet sections I and II are separate function bending magnets, their gaps 46, 45 and 45' are uniform in cross-section axially across the pole faces of the magnets and open-ended parallelepipeds longitudinally along orbit 11.

Coils 51 are again energized to receive the injected particles in the outer first beam orbit from injector 61 while the formerly captured beam circulates simultaneously in tube 53 in the inner third orbit. By subsequently, slowly de-energizing both split magnet coils 51 and 51 the two beams merge into one dense combined beam, as indicated by magnetic probes 41 and 41' and may be impacted into a target in tube 53 or extracted therefrom as is conventional. Suitable magnetic means 63 are suitable for this purpose. The control for maintaining the proper field strength has a suitable program and servo-system in connection with the electrostatic probes described for separate beams for adjusting the field strength in accordance with the momentum of the particles and position of the beam.

It is possible, in another embodiment, to circulate two beams in opposite directions, in one or more tubes 53 and then collide them. This may be accomplished by injecting two beams into the inner and outer first and third orbits before the coils 51 and 51' are de-energized to merge the two beams as described above.

It will also be understood from the above, that since the storage ring of this invention and the AGS injector therefor are substantially comparable in operation, size and construction, the orbits of the main bending magnets of the AGS having hyperbolic poles may be shifted by the split magnets of this invention.

In still another embodiment the fields and positions of the described magnets are adjusted so that straight equilibrium orbit, instead of the circular orbit of orbit 11, in a straight vacuum enclosure tube, instead of the endless configuration of tube 53, so as to provide straight inner, outer and central equilibrium beam axes.

This invention provides a method and apparatus for the injection, displacement, stacking and merging of high energy charged particles in separate and high intensity beams. These beams have circular, straight, curved and colliding orbits and provide a system for storing the beams for long periods of time. Additionally, standard equipment is utilized and multi-turn injection, betatron phase space stacking and low energy spread is achieved simply, easily and economically.

What is claimed is:

1. Particle handling apparatus for use with a strong focused beam of charged particles traveling in an evacuated chamber, comprising focusing means consisting of a system of quadrupole strong focusing first magnets, separate function bending second magnets for producing a particle bending first field for providing an initial endless particle equilibrium axis, and third magnetic means between said first and second magnets for selectively changing the strength of said first field for selectively displacing said equilibrium axis from its initial position, said third magnetic means consisting of split separate function bending magnets having first portions transverse to said axis for selectively maintaining said equilibrium axis outwardly in an enlarged diameter circle and second portions transverse to said axis for maintaining said equilibrium axis inwardly in a reduced diameter circle.

' 2. Apparatus as set forth in claim 1 wherein the third magnetic means consists of at least one split separate function bending magnet having a first portion forming first poles transverse to said axis for selectively shifting said equilibrium axis outwardly in an enlarged diameter circle, and a second portion forming second poles opposite in sign and adjacent to said first poles transverse to said axis and azimuthally equally spaced therewith from said first and second magnets for shifting said equilibrium axis inwardly in a reduced diameter circle.

3. Apparatus as set forth in claim 1 including means for selectively introducing particles into said beam in operable association with said magnetic means for sequentially receiving, stacking and merging several beams for storing said particles in a single high intensity beam.

4. A method for displacing the equilibrium axis of a strongly focused beam of charged particles traveling in an evacuated tube, said beam being directed by a separated, parallelepiped shaped, longitudinally extending, uniform, bending field that determines the direction and position of said axis, comprising decreasing said field strength on one side of said axis for receiving and transmitting said particles in a first beam in a first outer orbit, increasing said field strength on said outside of said axes for centralizing said first beam in a second central orbit, increasing said field strength on the opposite side of said axis from said first side thereof for receiving and transmitting said first beam in a third inner orbit, and decreasing said field strength on said one side again for receiving and transmitting a second beam in said first outer References Cited UNITED STATES PATENTS 2,394,070 2/1946 Kerst 328233 2,892,962 6/1959 Ross 335-210 3,021,445 2/1962 Wideroe et al. 335210 3,120,609 2/1964 Farrell 335-210 3,303,426 2/1967 Beth 31362 DAVID J. GALVIN, Primary Examiner.

JAMES W. LAWRENCE, Examiner.

20 S. A. SCHNEEBERGER, Assistant Examiner. 

1. PARTICLE HANDLING APPARATUS FOR USE WITH A STRONG FOCUSED BEAM OF CHARGED PARTICLES TRAVELING IN AN EVACUATED CHAMBER, COMPRISING FOCUSING MEANS CONSISTING OF A SYSTEM OF QUADRUPOLE STRONG FOCUSING FIRST MAGNETS, SEPARATE FUNCTION BENDING SECOND MAGNETS FOR PRODUCING A PARTICLE BENDING FIRST FIELD FOR PROVIDING AN INITIAL ENDLESS PARTICLE EQUILIBRIUM AXIS, AND THIRD MAGNET MEANS BETWEEN SAID FIRST AND SECOND MAGNETS FOR SELECTIVELY CHANGING THE STRENGTH OF SAID FIRST FIELD FOR SELECTIVELY DISPLACING SAID EQUILIBRIUM AXIS FROM ITS INITIAL POSITION, SAID THIRD MAGNETIC MEANS CONSISTING OF SPLIT SEPARATE FUNCTION BENDING MAGNETS HAVING FIRST PORTIONS TRANSVERSE TO SAID AXIS FOR SELECTIVELY MAINTAINING SAID EQUILIBRIUM AXIS OUTWARDLY IN AN ENLARGED DIAMETER CIRCLE AND SECOND PORTIONS TRANSVERSE TO SAID AXIS FOR MAINTAINING SAID EQUILIBRIUM AXIS INWARDLY IN A REDUCED DIAMETER CIRCLE. 